Field of the Invention
The invention relates to a system comprising a device for neural stimulation of a patient's cochlea and a programming unit for adjusting the stimulation device.
Description of Related Art
The sense of hearing in human beings involves the use of hair cells in the cochlea that convert or transduce acoustic signals into auditory nerve impulses. Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded. These sound pathways may be impeded, for example, by damage to the auditory ossicles. Conductive hearing loss may often be overcome through the use of conventional hearing aids that amplify sound so that acoustic signals can reach the hair cells within the cochlea. Some types of conductive hearing loss may also be treated by surgical procedures.
Sensorineural hearing loss, on the other hand, is caused by the absence, destruction or malfunction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. People who suffer from sensorineural hearing loss may be unable to derive significant benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is. This is because the mechanism for transducing sound energy into auditory nerve impulses has been damaged. Thus, in the absence of properly functioning hair cells, auditory nerve impulses cannot be generated directly from sounds.
To overcome sensorineural hearing loss, numerous auditory prosthesis systems (e.g., cochlear implant (CI) systems) have been developed. Auditory prosthesis systems bypass the hair cells in the cochlea by presenting electrical stimulation directly to the auditory nerve fibers. Direct stimulation of the auditory nerve fibers leads to the perception of sound in the brain and at least partial restoration of hearing function.
To facilitate direct stimulation of the auditory nerve fibers, a lead having an array of electrodes disposed thereon may be implanted in the cochlea of a patient. The electrodes form a number of stimulation channels through which electrical stimulation pulses may be applied directly to auditory nerves within the cochlea. An audio signal may then be presented to the patient by translating the audio signal into a number of electrical stimulation pulses and applying the stimulation pulses directly to the auditory nerve within the cochlea via one or more of the electrodes.
Typically, the audio signal, which usually is captured by a microphone, is divided into a plurality of analysis channels, each containing a frequency domain signal representative of a distinct frequency portion of the audio signal, wherein the frequency domain signal in each analysis channel may undergo signal processing, such as by applying channel-specific gain to the signals. The processed frequency domain signals are used for generating certain stimulation parameters according to which the stimulation signals in each stimulation channel is generated. The analysis channels are linked to the stimulation channels via channel mapping. The number of stimulation channels may correspond to the number of analysis channels, or there may be more stimulation channels than analysis channels, or there may be more analysis channels than stimulation channels. Various stimulation strategies are used, such as current steering stimulation (in order to maximally excite a stimulation site located in between areas associated with two or more electrodes) and N-of-M stimulation (wherein stimulation current is only applied to N of M total stimulation channels during a particular stimulation frame).
An example for such a CI system with electrical cochlea stimulation is described in International Patent Application Publication WO 2011/032021 A1 and corresponding U.S. Pat. No. 8,422,706.
Typically, neural stimulation of the cochlea occurs by electric pulses applied via an electrode array implanted within the cochlea; alternatively or in addition neural stimulation of the cochlea may occur via light pulses or heat pulses applied within the cochlea.
For electric stimulation CI devices deliver trains of electrical pulses via an electrode array implanted within the cochlea which evoke neural responses in the auditory nerve. In present systems, pulse shapes are typically biphasic, with equal current amplitudes and durations of the positive and negative phase and with an optional gap in-between the two phases.
The basic functioning of the electrodes and integrity of electrode-nerve interface can be assessed by measurements of the auditory nerve response elicited by electrical stimulation. Electrically-evoked compound action potentials (ECAPs) can be recorded on the intracochlear electrodes and sent back to the implant external processor by back-telemetry. The ECAP is a voltage signal that comprises a negative and smaller positive peak; the typical order of magnitude of the ECAP is between 50 and 500 microvolts. To a first approximation, the ECAP magnitude is monotonically related to the amount of auditory nerve fibers that responded to the stimulus. Cochlear implant manufacturers have developed software tools to easily set stimulation and recording parameters and monitor the corresponding ECAP response. Examples of such neural response measurements are found in U.S. Pat. No. 7,282,877 B1. Another measure of the evoked neural activity is the auditory brain stem response (ABR) which may be recorded via external scalp electrodes.
The article “Efficiency analysis of waveform shape for electrical excitation of nerve fibers” by A. Wongsarnpigoo et al., in IEEE Trans Neural Syst Rehabil Eng 18(3), 2010, pages 319 to 328, relates to a study wherein, using a population model of mammalian axons and in vivo experiments on the cat sciatic nerve, the effects of waveform shape and duration on the charge, power and energy efficiency of neural stimulation were investigated.
U.S. Pat. No. 6,751,505 B1 relates to a CI system wherein the stimulation rate and the operation mode, including the staggering order of the pulses, are adjusted according to the neural response to the pulses which is measured in-situ by neural response telemetry utilizing the electrode array.
International Patent Application Publication WO 2010/150002 A1 and corresponding U.S. Patent Application Publication 2012/0130449 relate to a CI system wherein the wave shape of the pulses depends on the location of the electrode; it is mentioned that by varying the waveshape between its normal and inverted versions the effectiveness of the neural stimulation can be varied in location between a position close to the driven electrode and a position close to the reference electrode.
U.S. Pat. No. 6,219,580 B1 relates to a CI system comprising a pulse table for defining the stimulation pattern.
U.S. Pat. No. 7,974,697 B2 relates to an implantable neural stimulation device, wherein stimulation signal parameters are adjusted according to a brain map obtained by using a medical imaging device.
The article “Effects of waveform shape on human sensitivity to electrical stimulation of the inner ear” by A. van Wieringen et al., in Hearing Research 200 (2005), pages 73 to 86, relates to a study on how thresholds and dynamic ranges of CI users can be controlled by manipulating the way in which the charge produced by the initial phase of an electrical is recovered, wherein different types of pulses are investigated.
The article “Effect of electrical pulse shape on AVCN unit responses to cochlear stimulation” by J. A. Wiler et al., in Hearing Research 39 (1989), pages 251 to 262, relates to a study on the effect of electrical pulse shape on stimulation of guinea pig cochlea.
The article “Asymmetric pulses in cochlear implants: effects of pulse shape, polarity and rate” by O. Macherey et al., in JARO 7 (2006), pages 253 to 266 relates to a study on the perception effects of the shape, polarity and rate of asymmetric pulses.
The article “Forward-masking patterns produced by symmetric and asymmetric pulse shapes in electric hearing” by O. Macherey et al., in J. Acoust. Soc. Am. 127 (1), 2010, pages 326 to 338 relates to a study concerning forward-masking experiments with varying pulse shapes.
The article “The perceptual effects of inter phase gap duration in cochlear implant stimulation” by C. M. McKay at al., Hearing Research 181 (2003), pages 94 to 99 relates to a study on the effect of interphase gap duration on loudness perception.